Lung P01 Competing (1/25/17) Project 2 (Rosen, PI) ABSTRACT This project is focused on the development of effective therapies for lung tumors driven by activation of the ERK signaling pathway, particularly those in which the pathway is driven by mutations in the KRAS or BRAF proto-oncogenes. These tumors are particularly difficult to treat, in part because there are no direct inhibitors of mutant KRAS or of dimer-dependent non-V600 BRAF mutations or fusions; in part because of adaptive resistance to RAF or MEK inhibitors, which is mediated by relief of ERK dependent feedback; in part because BRAF V600 tumors develop acquired resistance; and because of the toxicity of MEK inhibitors. In the last funding period we made material progress in overcoming these obstacles. We discovered that BRAF mutants fall into three functional classes based on their mechanism of activation; developed specific mechanism-based methods of inhibition of each class of mutant; identified novel equipotent inhibitors of RAF monomers and dimers for the treatment of Class 1 and 2 RAF mutants; identified MEK inhibitors with an enhanced ability to inhibit MEK driven by mutant RAS; and characterized and determined the mechanism of action of direct inhibitors of KRAS G12C, the most common mutant RAS allele in lung cancer. The goal of the proposal is to use these inhibitors to understand the role of each of these oncoproteins in lung cancer and pursue their preclinical development. Aim 1 concerns the use of the RAF dimer/monomer inhibitor to understand the role of Class 2 dimer-dependent BRAF mutants and to develop treatment regimens for Class 1 and 2 mutants. Aim 2 concerns the study of Class 3 BRAF mutants, the most common class in lung cancer, and exploits a novel mechanism for inhibiting their activity. Aim 3 concerns the preclinical development of the KRAS G12C inhibitor and its use to study the functional role of mutant RAS in lung cancer and the consequences of its inhibition. Inhibiting ERK signaling driven by any of the mutants is expected to relieve ERK-dependent feedback inhibition of signaling and contribute to adaptive resistance. In collaboration with RP4, we will undertake the study of this process for each of these methods of inhibiting RAS/RAF/MEK signaling, attempt to identify pathways required for tumor cell survival, and develop combination therapy on this basis.